GALT (gut-associated lymphoid tissues) will be studied for the presence of different T-lymphocyte subsets in experimental animals immunized or tolerized by the oral or parenteral route and in normal controls, and these cells will be enumerated and characterized as to size, density, adherence properties, proliferation, and antigenic markers. The presence, number, and character of nonspecific and specific suppressor cells in GALT under different circumstances of exposure to antigen and their mode of action will be investigated. Evidence will be sought whether antigen-antibody complexes, notably involving IgA or IgE antibody, play a role in activation of GALT suppressor cells. In specific immunological tolerance induced by the oral route, the distribution and migration patterns of the responsible suppressor cell population(s) will be studied. The mechanism of IgA and IgE "switching" of GALT B-cells, cultured under simplified conditions, will be investigated.